This application corresponds to French application No. 99 07997 filed Jun. 23, 1999, the disclosure of which is incorporated herein by reference.
The invention relates to an automatic gun with a membrane used to spray products, in particular to spray paint, abrasives or enamel, hydrosoluble or dissolved in a solvent.
There exist spray guns in which the spraying of the product is obtained exclusively by hydrostatic means, which is to say by applying a pressure to the product and causing it to exit through a nozzle at the front end of the gun. The spraying can also be obtained by pneumatic means, but generally, recourse is had to a combination of the two, which is to say that the spraying by hydrostatic means is combined with compressed air jets which, in addition to a central air spray jet, serve to adjust the shape and/or the size of the jet of sprayed product.
To adjust the supply of the product toward the nozzle and above all to cut off the supply when the gun is not actuated, conventional automatic guns without a membrane use a plunger which closes the outlet of the product through the nozzle. Retraction of the plunger to free this outlet is controlled by pneumatic control means which act on the piston of a jack moving the plunger rearwardly. When the control means are no longer actuated, a return spring acts on the jack in the opposite direction to move the plunger forwardly so as to close the outlet.
The invention relates more particularly to automatic guns with a membrane in which the membrane is controlled by pulsed air such that the product, which is supplied to the gun under constant pressure, leaves the nozzle in an intermittent spray.
In known automatic guns with a membrane, the membrane is driven in oscillatory movement by pneumatic control means for the pulsed closure of the supply of the product comprising a pulsed air supply which communicates with an annular chamber formed in the body of the gun about the rod of a control piston which, when it is actuated by pulsed air, is moved rearwardly against the action of a resilient return means. The piston thus carries out a reciprocating movement at the frequency of the pulsed air.
The forward end of the piston rod rests against the membrane, in a central region of the latter, so as to impart to it an oscillatory movement. The product to be sprayed is supplied under pressure to a reception chamber for the product which is located immediately before the membrane and which rearwardly is delimited, by the latter. This reception chamber communicates through a central opening with a central supply channel for the product arranged in the spray head and which opens directly into the nozzle.
When the control means for the pulsed air is not actuated, and also between two successive pulses, the central opening is closed by intermittent closure means constituted by the membrane itself which then is pressed by the end of the piston rod against the peripheral region about the opening which thus forms a seat. For this purpose, the diameter of the end of the piston rod is substantially greater than the internal diameter of the opening.
However, this seat is thus located at one of the ends of the central channel whose opposite end opens into the nozzle, which means that when the control means for the pulsed air is not actuated, which is to say when the spraying is stopped, all the volume of the central channel constitutes a residue of the product whose flow through the nozzle cannot be prevented, thereby giving rise to soiling.
Another drawback of this gun resides in the fact that the closure and the freeing of the opening toward the central channel during oscillation of the membrane are imprecise and do not permit good operation of these intermittent tent closure means for the supply of the product under constant pressure at frequencies which in this technical field are considered as high and which are of the order of 4 Hz.
This spray gun with a membrane moreover comprises means for the supply of pulsed spray air opening adjacent the spray nozzle to improve the spraying and to form the jet of the product. The spray air is supplied independently of the pulsed output of the product with the help of a programmable dispenser which supplies the spray air into an annular chamber formed in the spray head and which communicates with a first set of openings or outlet tubes for air opening quite near the outlet of the nozzle and with a second set of openings located in a ring at the forward end of the body of the gun. This arrangement permits the openings of this second set of openings to direct jets of spray air at a much greater angle toward the jet of product leaving the nozzle.
However, this independent supply of spray air requires an entire assembly of additional circuits and moreover, the dispenser which controls the spray air supply requires complicated and costly adjustments, which constitutes a further very great drawback.
A general problem associated as well with membrane spray guns as with the others which operate with a plunger, resides in the fact that certain pieces are very exposed to wear, in particular when the product is an abrasive product such as a paint comprising enamel. This affects first of all the nozzle, but also the membrane in the case of membrane spray guns and the plunger in the case of plunger spray guns. All these wear members thus require regular replacement which must take place more or less frequently as a function of the abrasive character of the product. It is thus desirable to be able to prolong the lifetime of these wear pieces and/or to facilitate their replacement.
The invention has for its object to overcome all these drawbacks mentioned above by providing an automatic membrane gun which avoids soiling by flow of a residue of the product when the gun is stopped, which operates without the problems at a high frequency with a free and immediate response to the pulsations of the membrane, which is provided with a simple spray air supply and of which at least certain of the wear members are designed so as to permit increased lifetime and/or easy replacement.
The object of the invention is an automatic membrane spray gun for the spraying of a product such as a paint supplied under constant pressure to the gun, comprising pulsed spray means for the product comprising an oscillation member associated with intermittent closure means for the supply of the product toward a nozzle, and control means of said pulsed spray means for the product, characterized in that said closure means comprise a plunger secured to the membrane and passing through the latter so as to be connected to a pulsation control member.
According to other characteristics of the invention:
the plunger is fixed to the membrane by gripping means disposed on opposite sides of the membrane;
the gripping means are constituted by clamps secured to the plunger and disposed on opposite sides of the membrane so as to grip it between them;
the forward end of the plunger extends into a central channel provided in a spray head, and the plunger can come into bearing against a seat arranged in the central channel immediately behind the nozzle;
in a gun of the type comprising pulsed air supply means for spraying, opening adjacent the spray nozzle, and control means for said pulsed air supply means for spraying, said control means of said pulsed spray means of the product comprise also said control means of said pulsed supply means for the spray air;
the end of the plunger is constituted by an interchangeable ferrule;
the ferrule of the plunger is of synthetic resin;
on the side in contact with the product, the membrane is clad with a layer of polytetrafluorethylene.